Unique, common, and interacting cortical correlates of thirst and pain

Abstract

This study used positron-emission tomography to establish the patterns of brain activity involved in the isolated and concurrent experiences of thirst and pain. Ten subjects were scanned while experiencing pain evoked with noxious pressure, while experiencing thirst after the infusion of hypertonic saline, and while experiencing pain when thirsty. After the onset of thirst, noxious pressure evoked more intense sensations of pain. Noxious pressure did not change subjective ratings of thirst. Thirst caused activation in the anterior cingulate (Brodmann area 32) and the insula. Enhanced pain responses were associated with increased activity in cortical regions that are known to correlate with pain intensity, and also with unique activity in the pregenual anterior cingulate and ventral orbitofrontal cortex. These findings suggest a role for limbic and prefrontal cortices in the modulation of pain during the experience of thirst.interoception ͉ neuroimaging S ensations determined by interoceptors guide behaviors that maintain homeostasis. Experiences such as thirst, hunger, pain, and temperature sensation reflect imbalances of the internal state and have important implications for survival (1, 2). Interoceptive sensations can occur in tandem and create conflicts that are not resolved by a single behavior. Prevailing circumstances determine which internal imbalance requires the most urgent attention. Interoception would be more consistent with survival if competing sensations were modified to reflect relative priorities. To investigate competing interoceptive sensations, we measured brain activity during painful pressure and thirst, both in isolation and occurring concurrently.Changes in sensations determined by interoceptors in response to changing environmental circumstances can be described as context-dependent responses (3). Both appetitive and aversive drives shape the state of an organism, and these drives must be reconciled to make the most adaptive behavioral choice. The juxtaposition of pain and thirst is particularly suited to the investigation of human brain activity associated with contextdependent changes in responses to competing drives. Both pain and thirst can be manipulated in a time frame compatible with imaging protocols, the former being particularly amenable to rapid onset and offset. There is evidence that the respective sensations are modified by contextual factors, although pain and thirst have yet to be examined contemporaneously. Finally, the concurrence of conditions likely to stimulate osmoreceptors and nociceptors would conceivably be associated with conflicting implications for behavioral responses. Drinking can be deferred without detrimental effect, but ultimately thirst must be sated to avoid desiccation. The acute onset of pain has more immediate implications for tissue integrity than the early experience of thirst. For example, during mild to moderate thirst, withdrawal from noxious stimuli would be more likely if thirst is decreased and͞or pain is increased. Furthermore, the opposit...

Regional brain responses associated with drinking water during thirst and after its satiation

“…From the very first neuroimaging study of thirst (16), this region has consistently shown activation in response to thirst using different imaging techniques (i.e., PET, arterial spin labeling) and varied experimental manipulations of physiology (17)(18)(19). In addition to being involved in the neural representation of thirst, the pACC is also part of the cortical network involved in swallowing (20,21), and in monkey it has been demonstrated that the cingulate cortex has cortical projections to pons (22), an area that contains nuclei implicated in the initiation of swallowing (23,24).…”

“…S2). Ratings of thirst were made using a 0-10 rating scale according to a previously reported procedure (18). The level of cycling exercise was standardized by calculating the heart rate reserve (HRR) for each participant: HRR = (220 -age in years) -resting heart rate (RHR), and then ensuring that participants maintained their heart rate at the sum of the RHR plus 60% of the HRR for the duration of the exercise period, using feedback on their heart rate provided by a telemetric device.…”

Effect of aging on regional cerebral blood flow responses associated with osmotic thirst and its satiation by water drinking: A PET study

“…Previous reports from this group have identified activations associated with thirst (13,14,26) and plasma Na (27) in two regions of the cingulate cortex: the pACC and the aMCC (summarized graphically in ref. 28).…”

“…The contrast between maximum thirst and baseline revealed two loci of activation in the cingulate cortex in both groups: the aMCC [Y, (12,24,26); O, (12, 18, 48); Talairach coordinates] and the pACC (BA32) [Y, (8,38,2); O, (14,36,14)] (Fig. 2).…”

Overdrinking, swallowing inhibition, and regional brain responses prior to swallowing

“…S1A). Ratings of thirst were made by using a 0-10 rating scale (with 0 indicating thirst and 10 indicating maximum thirst) according to a previously reported procedure (74). The degree of exercise was standardized by (i) calculating the heart rate reserve (HRR) for each participant before exercise [HRR = (220 − age in years) − resting heart rate (RHR)]; (ii) adding 60% of the HRR to the RHR; and (iii) ensuring that each participant maintained their heart rate at this value (RHR + 0.6*HRR) for the duration of the exercise period by using feedback on their heart rate provided by a telemetric device.…”